Immunization refers to the targeted development of immunity to a specific viral or bacterial pathogen. A distinction is made between active and passive immunization. In immediately effective passive immunization, the body is directly supplied with antibodies against the antigens of a particular pathogen, whereas in active immunization the immune system must first build up the antibodies itself through direct contact with inactivated pathogens.
What is immunization?
Immunization refers to the targeted buildup of immunity to a specific viral or bacterial pathogen. Immunization involves the enhanced ability of the immune system to effectively fight a defined viral pathogen type, and in a few cases a bacterial pathogen, in the future. An existing infection can thus be overcome or contact with the pathogen can no longer trigger the infectious disease, as a specific and individual immunity exists. This is always an acquired immunity, which is achieved via active or passive immunization. In active immunization, the body – and thus the immune system – is confronted with the pathogen and its antigen, which has previously been rendered harmless in a suitable form. The immune system then (actively) develops a specific antibody whose “recipe” is stored in memory cells of the immune system (immunological memory). Upon renewed contact with the specific pathogen, the immune system is able within a very short time to synthesize antibodies in sufficient quantity to kill the pathogen or otherwise render it harmless. Strictly speaking, an accidental contact of the immune system with a specific pathogen that the immune system has overcome also counts as active immunization. It is contrasted with passive immunization, which achieves directly effective protection as a preventive measure against infection or even overcomes an existing infection. It involves the direct supply of the body with the necessary antibodies against the specific pathogen.
Function and task
The particular benefit of active immunization is that the immune system is given sufficient time to develop the specific antibody after contact with the inactivated pathogen or antigen, without allowing the pathogen to win the “race.” Active immunization, which is usually carried out in the form of vaccination, has made it possible to sustainably contain many epidemics that used to claim thousands of victims. In some cases, pathogens have been temporarily controlled worldwide in such a way that no more cases of disease have occurred. However, it cannot be ruled out that localized populations of the pathogens in question may exist in reservoirs without becoming conspicuous. Because active immunization involves immune system reactions and the immune system does not distinguish between contact with inactivated or infectious germs, the antibodies produced are stored in the immune system’s “database” in the form of the memory cells, so that if contact is made again with the same – this time activated – pathogen, the antibodies can be synthesized very quickly and the disease cannot break out. Since the initial production of the specific antibodies takes a certain time of several days to weeks, active immunization is usually not suitable for the treatment of an already existing acute infection. Rather, it serves as a preventive measure against certain pathogens, for example before traveling to the tropics or before planned trips to endemic areas. Active immunization is carried out either by oral ingestion of the attenuated live pathogens or by injecting “dead” pathogens or by scratching the skin (smallpox viruses). In order to also achieve an immediately effective defense against pathogens during the acute infection phase, the necessary antibodies, which have been isolated or produced elsewhere, can be injected directly. This has the advantage of immediate effect, but also with direct involvement of the immune system. This means that the antibodies are completely degraded after some time and their existence is not stored in memory cells. In the event of renewed contact with the pathogen, the immune system cannot remember the effective antibodies.This means that no long-term protection can be built up by passive immunization. In some cases, such as for the treatment of tetanus and rabies infections, a combination of passive and active immunization is possible (simultaneous immunization).
Diseases and medical conditions
Diseases and illnesses that may be associated with immunization are very rare. Accordingly, the risks associated with immunization are low. Residual risks do exist, however. In active immunization by oral ingestion of the attenuated pathogens (oral vaccination), there are basically two different basic risks. On the one hand, there is a small risk that the hoped-for immune response to the germs will not occur, because the person suffers from an acute diarrheal illness, which means that the germs cannot adhere to the intestinal epithelium and are eliminated unnoticed by the immune system. A further – very small – risk exists for persons in the environment of the vaccinated person. They can become infected by the excreted live germs of the vaccinated person if they come into contact with the germs and at the same time have an extremely weakened immune system. Active vaccination by hypodermic needle carries the normal risks associated with any injection. This may include reactions such as fever, headache and aching limbs, similar to a mild flu. You may also experience the symptoms that would occur if you were infected with the vaccinated pathogen. However, symptoms and course are much weaker and usually harmless. De facto, however, the patient is easily infected after vaccination. Children and adults who suffer from an acquired or inherited immune deficiency or are artificially immunosuppressed must not be vaccinated. In addition, redness and immune reactions at the injection site may occur and disappear. Side effects associated with passive immunization beyond the normal risk of a reaction to needle insertion are not known.
